The threat was posted to Instagram by user "blaxckhood," police say. A photo showed only a black box with the caption, "I am going to shoot up Monticello High School, Middle school/ elementary school on 9/21/18 get ready!"

Monticello school officials were made aware of the social media post and decided to close the school district on Friday.

"Out of an abundance caution, all MCSD schools will be closed tomorrow, Friday, Sept. 21, as we continue to investigate an online threat and request subpoenas for tracking electronic communication and IP addresses," the Monticello Central School District wrote on its website late Thursday night.

All after-school activities including the Empire Program were also canceled and there was no school for any Monticello students who attend school in other locations.

The Monticello Police Department is asking residents to stop calling the station to report the threat. Police are aware and need all of their manpower to continue their investigation into the threat, police say.

Anyone with information on the threat is urged to call the Monticello Police Department or the Sullivan County Sheriff's Office.